Why did I say racial hierarchy was “maintained or reconstructed”?

Because emancipation destroyed slavery as a legal institution, so racial hierarchy could no longer operate through exactly the same legal mechanism.

Therefore, after slavery:

some existing racial hierarchies could be maintained, while others could be reconstructed through new institutions and practices.

For example:

Before emancipation:

racial domination → slavery.

After emancipation:

racial domination → segregation + disenfranchisement + violence + discriminatory economic relationships, etc.